28 



Geographic 



Distrihution of 



Communities: 



Marine Biomes 



Tlif geographic ilistribiitioii of organisms in tlie 

 sea depends on tlieir resjionses to currents, temper- 

 atures, and i)liysical l)arriers ; local distribution is 

 affected by waves and tides, type of bottom, salinity, 

 and depth. Marine ecology is concerned with envi- 

 ronmental factors and jiroblems of organismic ad- 

 justments quite different from those on land and 

 also different in many respects from those in fresh- 

 water. Animals are relatively more conspicuous than 

 plants. Succession is less evident, but such ecological 

 processes as represented by chemical cycles, cooper- 

 ation and disoperation. food chains, productivity, 

 population dynamics, niche segregation, speciation, 

 and dispersal are fully as important as on land. 



Distinct self-contained community units are more 

 difficult to recognize in the sea than on land because 

 of the apparently greater interrelation of benthic 

 species and the freer movement with circulating cur- 

 rents of plankton and nekton. Plankton is every- 

 where a basic link in food chains, but the general 

 distribution and importance of plankton species in 

 the sea is no more remarkable than that of soil organ- 

 isms in terrestrial biomes. To consider the entire 

 ocean community as a single biome. as has been sug- 

 gested by some investigators, is stretching the concept 

 beyond its usefulness. Since we identify biomes by 

 differences in the life-forms and functional adjust- 

 ments of the conspicuous dominant or predominant 

 organisms, we may properly recognize biomes that 

 occur in the open ocean, on eroding rocky shores, on 

 muddy and sandy beaches, and composing the coral 

 reefs and atolls. Each of these biomes may be subdi- 

 vided by the taxonomic composition of the predomi- 

 nant organisms into secondary communities equiva- 

 lent to the biociations that we have recognized on 

 land. Much of the early literature on marine com- 

 munities has been reviewed by Gislen (1930). 



We can only hope in this chapter to present a 

 brief summary of some of the more salient features 

 of marine ecology. For more thorough treatments, 

 the reader is referred to the publications of Sverdrup 

 et al. (1942), Ekman (1953), Harvey (1955), 

 Hedgpeth (1957), and Moore (1958). 



H.4BITAT 



The marine biocycle is considered to have 

 benthic (bottom) and pelagic (open water) divisions. 

 The littoral cone of the ocean shore extends between 

 the limits of high and low tides. The sublittoral zone 

 covers the continental shelf to a depth of about 200 m, 

 the approximate depth at w4iich maximum wave ac- 

 tion jjroduces any effect. The average depth of the 

 ocean is about 3800 m, but oceanic trenches (hadal 

 zone) extend much deeper; the Marianas Trench in 

 the Pacific Ocean to approximately 11,600 m. The 



351 



